The present invention provides a cationic lipid, which allows a nucleic acid to be easily introduced into a cell, etc., represented by formula (A) (wherein: R1 is alkenyl, etc., R2 is alkenyl, etc., R3 and R4 are alkyl, or are combined together to form alkylene, or R3 is combined with R5 to form alkylene, R5 is a hydrogen atom, etc., or is combined with R3 to form alkylene, X1 is alkylene, and X2 is a single bond or alkylene), etc.； a composition comprising the cationic lipid and a nucleic acid, a method for introducing a nucleic acid into a cell by using the composition comprising the cationic lipid and the nucleic acid, and the like.本發明提供一種容易地將核酸導入至例如細胞內等之下述式(A)所表示之陽離子性脂質等、含有該陽離子性脂質及核酸之組合物、及使用含有該陽離子性脂質及核酸之組合物而將核酸導入至細胞內之方法等。(式中，R1為烯基等，R2為烯基等，R3及R4為烷基，或者一併形成伸烷基，或者R3與R5一併形成伸烷基，R5為氫原子等，或者與R3一併形成伸烷基，X1為伸烷基，X2為單鍵或伸烷基)
